Warn user about unsaved changes when closing the Web IDE

[xpyctumo]

If the user makes any changes to files/file and does not save them, the user should be notified when closing the browser tab that these changes may be lost.

Note: It is important to show this warning only if the Web IDE actually has unsaved files in the active project

confirm("You will lose unsaved changes")

Now a user can close the tab and lose their unsaved changes